The present invention relates to an adaptive cruise control system, and more particularly to an adaptive cruise control system employing a strategy for determining an optimal amount of deceleration when traveling behind an in-path vehicle.
Cruise control systems for automotive vehicles have been available for years. Typically, for the basic systems, the vehicle driver attains the desired vehicle speed and initiates the cruise control system at a driver selected set speed. The vehicle then travels at the set speed unless the driver applies the brakes or turns off the system.
With advances in vehicle electronics and sensor technology, adaptive cruise control (ACC) systems are becoming available that not only maintain the set vehicle speed, but also include an object sensing technology, such as radar, laser or other type of sensing system, that will detect an in-path vehicle. If the host vehicle is following too closely behind an in-path vehicle, the ACC system will automatically reduce the host vehicle speed (by reducing the throttle and/or applying the brakes) sufficiently to obtain a predetermined safe following interval (which may be based on following distance and/or following time). This deceleration of the host vehicle is also known as the longitudinal response of the ACC system. After reaching its objective, the ACC system will then continue to maintain the safe following interval.
The host vehicle may also be at a greater distance behind an in-path vehicle, but traveling at a higher rate of speedxe2x80x94this requires the ACC system to decelerate the host vehicle so that it is no longer traveling at a higher rate of speed than the in-path vehicle. Some have attempted to control the rate of deceleration with a stand alone gain or a look-up table type of control strategy, but these are generally inadequate for employing with all combinations of relative speed and gap (also called range). For a look-up table, it is difficult to include the full dynamic ranges of both the positive gaps and the negative relative velocities in the adaptive cruise control range. For a stand alone gain, a typical deceleration limit is xe2x88x920.3 g for the host vehicle or the system may employ this deceleration limit as a function of relative speed, but this does not achieve a smooth host vehicle trajectory for many combinations of relative speed and gap. It is most desirable that the ACC system provide a deceleration that is acceptable to the vehicle occupantsxe2x80x94neither overreacting or underreacting when determining the appropriate rate of deceleration for the host vehicle, and providing a relatively smooth transition. Such an ACC system, then, can provide the most comfort to vehicle occupants without creating undue anxiety due to too fast of an approach to an in-path vehicle or too much deceleration when not necessary.
Thus, it is desirable to employ an adaptive cruise control system that employs a strategy for determining and implementing an optimal amount of deceleration, with a smooth speed trajectory, of a host vehicle while traveling behind another vehicle that is in its path.
In its embodiments, the present invention contemplates a method of determining an amount of deceleration for a host vehicle having an adaptive cruise control that is following behind an in-path vehicle. The method includes the steps of: determining a speed of the host vehicle and a speed of the in-path vehicle; determining a relative speed between the host vehicle and the in-path vehicle; determining a range between the host vehicle and the in-path vehicle; estimating a deceleration of the in-path vehicle; determining a deceleration of the host vehicle; calculating an instantaneous optimal deceleration amount needed to match the host vehicle speed with the in-path vehicle speed at a desired future range between the host vehicle and the in-path vehicle; and selectively changing the host vehicle deceleration in response to the calculated instantaneous optimal deceleration amount.
The present invention further contemplates a host vehicle having an adaptive cruise control system. The host vehicle includes a host vehicle speed determiner capable of determining a host vehicle speed, and an object detection sensing system capable of detecting an in-path vehicle and estimating a speed of the in-path vehicle, a range from the host vehicle to the in-path vehicle, and a relative speed between the host vehicle and the in-path vehicle. A host vehicle deceleration estimator is capable of estimating a current deceleration of the host vehicle, an in-path vehicle deceleration estimator is capable of estimating a current deceleration of the in-path vehicle, and an optimal deceleration estimator is capable of calculating an optimal deceleration amount based upon calculating an optimal deceleration amount needed to match the host vehicle speed with the in-path vehicle speed at a desired future range between the host vehicle and the in-path vehicle. The host vehicle also includes an adaptive cruise control controller capable of selectively changing the host vehicle deceleration in response to the calculated optimal deceleration amount.
Accordingly an embodiment of the present invention can employ a deceleration strategy in an ACC system that will use the calculated deceleration needed to match the host vehicle speed with the in-path vehicle speed at a final desired gap between the vehicles as the maximum deceleration boundaries of the ACC system.
An advantage of the present invention is that the adaptive cruise control system of the host vehicle can achieve a smooth host speed trajectory behind an in-path vehicle, especially in a case of high negative relative speed.
Another advantage of the present invention is that a desirable amount of deceleration, without generally overreacting or underreacting, is achieved by the adaptive cruise control of the host vehicle.
A further advantage of the present invention is that the adaptive cruise control system achieves an optimal use of the deceleration range to achieve any desired deceleration relative to an in-path vehicle.